The principal objectives of this project are to use mathematical modeling to improve understanding of the spread of gonorrhea and to use analytical methods and computer simulation to evaluate and compare present gonorrhea control procedures. Gonorrhea is different from other infectious diseases such as influenza and measles where the infective levels are limited by the buildup of immunes; consequently, new mathematical models for gonorrhea epidemiology must be used. An ordinary differential equation model which considers the factors which are epidemiologically significant for gonorrhea has been developed and analyzed by Lajmanovich and Yorke. The model involves a set of low and high risk groups of males and females and considers the contact rates between groups and the average period of infectivity of individuals in the groups. Currently available incidence data will be used to identify a specific set of low and high risk groups and to determine parameter values so that the equilibrium point for the model is consistent with observed infective levels in each group. The importance of high risk groups and of reinfections in the dynamics of gonorrhea spread will be determined. The major current gonorrhea control procedures are screening and contact investigation. Extensions of the general gonorrhea model corresponding to these procedures will be developed and current screening positivity rates and contact investigation effectiveness rates will be used. High risk group screening, general population screening and rescreening will be evaluated and compared by examining changes in screening extent or effectiveness. The optimum use of (potentially available) gonorrhea vaccines will be determined from a detailed model of sexual interactions and repeated contacts.